持久/恢复Scala实例（进出文件）

Question

在Scala中保存/恢复文件的最简单方法是什么？

现在scala.util.Marshal已被删除，并且创新的Pickling库似乎不受支持（需要使用Scala 2.10.4）。

示例：

val myObj = SortedSet(20, 10, 30)
SomeUtil.saveToFile(myObj)

//...later:
val restored: SortedSet[Int] = SomeUtil.restoreFromFile(filename)

Answer 1

这适用于Scala 2.11.1，但比我对现代类库的预期要麻烦得多：

的SaveToFile

def saveToFile (obj: Object, filename: String) = {
  val out = new FileOutputStream(new File(filename));
  try {
    out.write(Serializer.serialize(obj))
  }
  finally {
    out.close();
  }
}

restoreFromFile

def restoreFromFile[T] (filename: String): Option[T] = {
  try {
    val file = new FileInputStream(filename)
    val in = Stream.continually(file.read).takeWhile(-1 !=).map(_.toByte).toArray
    Some(Serializer.deserialize(in).get)
  }
  catch {
    case _: Exception => None
  }
}

object Serializer {

  def serialize[T] (obj: T): Array[Byte] = { // use instead of Marshal.dump in Scala 2.11
    val byteStream = new ByteArrayOutputStream()
    val out = new ObjectOutputStream(byteStream)
    out.writeObject(obj)
    out.close()
    byteStream.toByteArray
  }

  def deserialize[T] (data: Array[Byte]): Try[T] = { // use instead of Marshal.load in Scala 2.11
    if (data == null)
      Failure(new NullPointerException())
    else {
      val in = new ObjectInputStream(new ByteArrayInputStream(data))
      try {
        Success(in.readObject.asInstanceOf[T])
      }
      catch {
        case e: Exception => Failure(e)
      }
      finally {
        in.close()
      }
    }
  }
}

Answer 2

更简单的方法是使用Java类：ObjectInputStream和ObjectOutputStream。

使用@SerialVersionUID标记您的自定义类：

@SerialVersionUID(1L)
class MyClass extends Serializable {...}

保存

val out = new ObjectOutputStream(new FileOutputStream(new File(filename)))
out.writeObject(this)
out.close

恢复

val in = new ObjectInputStream(new FileInputStream(new File(filename)))
val myInstance = in.readObject().asInstanceOf[MyClass]
in.close